What is the correct option to complete the paragraph below?

The Battle of Tarawa was a disaster from the start. November 1943, their first big foray in the central Pacific Ocean, US forces invaded this atoll the Gilbert Islands, hoping to dislodge Japanese troops and push closer to Tokyo. But as soon as the assault began, it literally ran aground. Most of the landing boats smashed a shallow coral reef, forcing marines to flounder their way to shore Japanese gunfire. One in five US troops died in the batile - 300 the reef alone.

(Adapted from hitps://doi.org/10.1038/441586-022-02287-5)